This invention relates to drawing arcs, circles and lines and measuring angles and in particular, devices for accomplishing these tasks.
There are known devices for either drawing arcs and forming circles or for measuring and laying down angles, and there are some which are capable both of measuring angles and forming arcs and circles. However, these devices are unsuitable for the simultaneous drawing and measuring of an arc. Moreover, the known devices that can be used to form circles cannot readily measure angles beyond 180xc2x0.
Consequently, a need exists for a device which can be used to simultaneously draw and measure an arc and at any angle from 0xc2x0 to 360xc2x0.
Accordingly, an object of this invention is to provide a device which can simultaneously draw and measure an arc having one of an infinite number of possible radii and at any angle from 0xc2x0 to 360xc2x0.
The invention generally relates to a device for geometric construction with a marking instrument. The device comprises a radius arm, which includes a means for receiving the marking instrument and a disc having a pivot point, and a rotatable member attached to the radius arm around the disc, the rotatable member being movable through 360xc2x0 about said disc and having indicia for measuring degrees between 0xc2x0 and 360xc2x0.
In a preferred embodiment, the device has a radius arm and a rotatable member, which are rotatably attached by means of a disc. The radius arm includes this disc, which has a pivot point, and a means for receiving the marking instrument. The receiving means is adjustably spaced from the pivot point and further comprises an elongated opening within the radius arm. The elongated opening has a length and two straight edges substantially parallel with the elongated opening. The radius arm has measuring indicia along at least one of the two straight edges. A sliding member which is movable along the length of the elongated opening is also part of the radius arm. The sliding member includes at least one, and preferably two, pairs of pointers and at least one, and preferably two, holes for receiving the marking instrument, with each of said holes between a pair of pointers. The pairs of pointers indicate one of the measuring indicia. The sliding member further comprises a locking means to hold the sliding member in place along the elongated opening. The device also includes a rotatable member attached to the radius arm around the disc. The rotatable member is movable through 360xc2x0 about the disc and has indicia for measuring degrees between 0xc2x0 and 360xc2x0. The rotatable member further includes at least one radius hole in it for receiving the marking instrument. The disc comprises a top part and a bottom part, with the top part and the bottom part rotatably attaching together the rotatable member and the radius arm.